1. Field of the Invention
The present invention relates to a power system, and more particularly, to a power system having a power saving mechanism.
2. Description of the Prior Art
Along with the advantages of high efficiency, low power consumption, small size and light weight, the flyback power system has been widely employed as a power converter in various electronic products. Please refer to FIG. 1, which is a circuit structure diagram schematically showing a prior-art flyback power system 100. A rectifying circuit 102 and a filter capacitor 105 are employed to generate an input voltage Vin through performing rectification and filter operations on an alternating input voltage Vac provided by an alternating power supply 101. A transformer 120 comprises a primary winding 121 for receiving the input voltage Vin, a secondary winding 122, and an auxiliary winding 123. A first rectify/filter circuit 170 is utilized for performing rectification and filter operations on a preliminary output voltage Vop induced by the secondary winding 122 for generating a first output voltage Vo1 forwarded to a first load 195. A voltage regulation circuit 180 functions to regulate the first output voltage Vo1 for generating a second output voltage Vo2 furnished to a second load 196. A feedback circuit 140 is put in use for converting the second output voltage Vo2 into a feedback signal Sfb furnished backwards to a switch control circuit 130. A second rectify/filter circuit 190 is employed to perform rectification and filter operations on an induced voltage of the auxiliary winding 123 for generating a power voltage Vcc to power the switch control circuit 130. By making use of the feedback signal Sc, the switch control circuit 130 generates a control signal Sc for controlling on/off states of a switch 125, which in turn controls a current flowing through the primary winding 121.
Regarding the operation of the flyback power system 100, the first output voltage Vo1 for powering the first load 195 is significantly greater than the second voltage Vo2 for powering the second load 196. After entering a power-saving operation mode, only the second voltage Vo2 is required to continue powering the second load 196 while the first load 195 is not required to be powered. However, the first output voltage Vo1 is still retained to hold a high voltage level. Under such situation, the flyback power system 100 will waste redundant power for keeping the high voltage level of the first output voltage Vo1 and therefore the power efficiency of the power-saving operation mode is degraded.